Hi,
thanks for taking the time to investigate your issues with Talefish (and trying it, even)!

• the current behaviour you describe is the desired one: Talefish only saves you progress per "opened thing". If you open files separately (by tapping on it in the file selector, so basically making it a one-file-playlist), it should save the progress for every file. Within an opened directory, skipping to track beginnings is, as pichlo pointed out, the expected behavior by most users, so the player is not even remotely designed to do anything else.
• removing items from the playlist isn't supported, since it's a rather unusual use case for audio books. You could remove the file and re-open the whole directory, but please mind that this will currently likely mess up your saved progress, as well.
• while autodelete can be useful for a podcast player, I think it's a bit "dangerous" (well, better: possibly error prone) for an audiobook player.

Please don't apologise for contributing Ideas, those are always welcome! But please don't be sad, either, if I decide not to pursue them for one reason or another.

Edit: After reading peterleinchen's post, I kind of get where you're coming from. But in Talefish, the whole directory/playlist is considered the "Book", which can consist of several chapters/tracks. If you change the Book, the position will be saved, but if you just browse around in it, Talefish is thinking that you intend to "read" from another page, now.